There are a number of methods and apparatus for treating indoor air. Such air normally contains odors and particulate matter and various systems have attempted to control both problems.
Filtration is generally considered to be the separation of particles or solids from a heterogeneous mixture of a fluid, such as air. These solids or particles are removed from the air by forcing the air through a filter medium, or septum, upon which the solids are deposited.
It is well known that dust can be removed from the air by filters, electrostatic precipitation, washing of the air with a water spray, or dynamic precipitation. The first method, filtration, has been the most efficient and effective procedure for the removal of dust from indoor air. In general, air filters are used where the dust concentration is relatively low and does not exceed 4 g. per 1,000 cu. ft. of air. The filtering medium varies, and glass fibers, wire screen, steel wool, animal hair and hemp fibers have all been employed.
In addition to dust, indoor air contains numerous odorous pollutants, including formaldehyde, acetic acid, ammonia, hydrogen sulfide, sulfur dioxide and solvent gases such as benzene and toluene. Furthermore, such air often contains additional odors such as bathroom odors, kitchen odors, basement odors, tobacco odors and the like.
The most common method for removing these odors is ventilation or the supply of fresh air to and the removal of contaminated air from a space or room. Under very cold or very hot climatic conditions, ventilation is not desirable for obvious reasons.
Other methods exist for "masking" odors in indoor air by covering such odors with a fragrance or other pleasant-smelling material. These methods, however, do not remove the offensive odors from indoor air, but merely disguise them as non-offensive odors.
According to the prior art, indoor air treatment systems for the removal of odors have employed special liquids for the removal of odors as well as for inhibiting the growth of microorganisms, many of which are odor causing by themselves. While these air treatment systems have been effective to deodorize, such systems have been complex and expensive to operate, and lack both high capacity and high efficiency for removing a broad spectrum of pollutants including formaldehyde and other solvent gases, from indoor air.
Other specialized air purification systems have attempted to remove odors. The only practical method disclosed by the prior art of removing odors from air is by active carbon adsorption and this has been found useful against cooking, body and tobacco odors. While effective initially, active carbon loses its effectiveness over time, and also is not useful for removing the broad spectrum of odors generally encountered in a household environment.
Bacteria in the air stream presents another problem which requires the use of ultraviolet radiation or germicidal sprays for its removal. This technique, however, does not remove odors or particulate matter.
Thus, none of the prior art filters or filter elements are effective for the removal of a wide variety of odors and particulate matter from indoor air.
The present invention is directed to what can be termed air sanitation, the cleaning of air, whether the contaminating substance be dust, odors, fumes, or bacteria, and the applicant has surprisingly discovered combinations of dry or impregnated filter elements which provide increased deodorizing effectiveness or removal of a wide variety of odors and particulate matter from indoor air.